Water-resistant composition of matter



In the production of Patented .Fsn. i236 OLIVER W. STOREY AND KLIEFOTH,OF ISON, WISGOKSIR,

0. F. BURGESS LABORATORIEE, INC, 03 KADISON, wrsconsm, 5. OORPQBATIOE OEDELAWARE Ho Drawing.

The present invention relates to the 'production of a water-resistantcomposition of matter from a mixture of a ground filler and sodiumsilicate wherein the sodium silicate is' sued May 10, 1927) there isdescribed a porcus molded product which is produced by ufiing uickly anintimate mixture of a iiller an intumescent binder such as sodiumsilicate. A wall board made from this roduct is described in Weiss andNorris, erial No. 720,510,'June 17, 1924 (now Patent No. 1,655,718issued Jan. 10, 1928). the material described in those applications aden h-like mixture of an intumescent binder, suc as sodium silicate,anda filler, is first made. The doughlike mixture is heated rapidly in'amold or between paper facings on heated platens to form, a porous,rigid, coherent product. This product should preferably have a highresistance to Water or moisture to be most useful in the arts,especially as wall boards.

We have discovered that the maximum resistance to moisture is obtainedunder certain limiting conditions, these conditions being particle sizeof the ground filler, composition of sodium silicate solution, and ratioof sodium silicate to filler This discovery relates only to thosemixtures wherein the chemical state of the sodium silicate remainspractically unchanged in the final roduct and there is no appreciablereaction between the sodium silicate and filler. Not only does ourdiscovery apply to a pufi'ed product but it may also be applied to onewhich is not pufied. Our invention makes advantageous use of a groundlimestone fill? er. The term limestone covers the wide warna-ansrsraurcomrosrrron or an Application filed a ni 1, 1927. Serial No. reams.

variety of stones which may vary from 21- 1 most ure calcium carbonateto those high enoug in magnesium carbonate to be'known as dolomite. Weprefer using a"dolomitic limestone.

When the ordinary solution of sodium silicate of commerce, such as isobtainable in quantity on the market, is mixed in prop er proportionswith a powdered filler, and subjected to the action of heat at atemperature somewhat above the boilin point of water, the mass e ands,due to t e formation of steam, an pufis' into a porous mass. Thestructure or texture is similar to that of bread.

The ordinary solutions of sodium silicate of commerce are of necessityof such viscos ity that they will flow rapidl from contamers at roomtemperature. 's is especially true of those sodium silicates in whichthe SiO -Na O ratio varies between 2.6 to 1 and 3.4 to 1, the range towhich our invention has been applied. The maximum viscosity of thesecommercial soiutions in absolute units is less than 1000 centipoises at25 C. Inour invention we contemplate using, as a preferred embodiment,solutions having a viscosity of at least 2000 centipoises. In ourviscosity measurements the Stormer viscosimeter was used, this beincalibrated against castor oil, the viscosity 0 which was taken as 651centipoises at 25 C., this value being given on age 24 of TechnologicPaper No. 112 of the v ureau of Standards.

In general, it isnecessary to make a doughlike mass at room temperaturesto secure the best pufiing conditions. If athinner mixture is used themass becomes too thin when heated and the walls of the cavities collapseand a tion 0 cavities become stiff an filler is too lar e' the wails'ofthe the proper degree of porosity is not secured. It is preferable forthe manufacture of wallboard and other materials that the puiiedstructure should weigh less than 62% pounds per cubic ,foot. Not only dothe hysical characteristics of the structure de du 11 the proportion offiller to silicate o soda ut also 11 n the fineness of the filler,composition 0 the silicate of poor structure results. If the proporsodaand rapidity of pulling. We have discovered that the particle size ofthe filler determines largely the water-resistance of the final productprovided that all comparative products have been heated to the sametemrature. Our co-worker, A. W. Schorger, in application Serial No.103,391, April 20, 1926, shows that a temperature of at least 210 C; isneeded to give the best results with any particular mixture. At thistemperature the silicate of soda is nearly dehydrated. Our results,ashereinafter detailed, are based on heating orjheat treating at about210- C.

We consider that a sodium silicate and filler porous composition ofmatter has the proper water resistance if it withstands immersion inwater at a tem erature of 90 C for thirty minutes without ecoming soft.

We have discovered that if rock, or other solid material, such aslimestone, and pref-. erably dolomiticlimestone, is ground to a wder, asby a ball mill, the structure resultmg from use of this powdered fillerhas a water resistance depending largel upon the fineness of grinding.If a ground dolomitic limestone is used, such as is sold in considerablequantities for mixing in asphalt for aving purposes, the iwa'terresistance is low. uch a filler of which 82 er cent passes through a 200mesh screen, as an average article diameter or size of 12.1 microns.

his diameter is determined-by means of a microscope as described inTechnical Paper 296 of the U. S, Bureau of Mines, entitled Size andcharacter of grains ofnonmetallic mineral fillers. On an area basis sucha filler has a .high concentration. of particle surface on those grainshaving diameters between 2.5 and 20 microns. If the average particlesize is decreased somewhat by prolonged fine grinding the waterresistance 1s greatly increased and becomes sufiicient for mostpurposes. If the particle size is decreased by continued grinding sothat it is below about 11.0 microns the water resistance becomessatisfactory. Water resistance does not appear to be a direct inversefunction of particle size. A size which gives excellent results isbetween 9 and 10 microns or about 9.4 microns. We have used a veryfinely ground doloinitic limestone having an average particle diameterof 8.4 microns with excellent results. However, such exceedingly finegrinding is costly and it also increases the proportion of sodiumsilicate solution used, thereby increasing the cost. It is thereforedesirable to use the coarsest grind consistent with satisfactory waterresistance. Fillers which have given excellent results, both from thestandpoint ofcost and water resistance, have had a high concentration ofparticle surface between particle sizes of 0.8 and 10 microns,

the maximum concentration being between 2.5 and 5.0 microns. The grounddolomitic weaves cate when heated become very fluid and aweak friablestructure results which is entirely unsuited for most purposes, as forwallboards. When a filler is made by grinding a solid stone, such aslimestone, to a fineness comparable to clay, the same dificultiesappear. Our invention is therefore directed particularly to fillerswhich are made by grinding to within certain ranges of average particlesize and to mixtures of these with small amounts of the previouslmentioned porous or precipitated materia s where the final averageparticle size of the mixture mmains within the limits set by theappended claims.

The necessity of having a dough-like mix and sufiicient sodium silicateto secure proper pulling, limits the viscosity of the sodium silicatesolution which may be used. With sodium silicates having a ratioof SiOto Na O between 2.6 to 1 and 3.4 to 1 we have found that. it isnecessary to use a solution of sodium silicate which has a viscosity ofabout at least 2000 centipoises and a filler having an average particlesize of between 8.4 and -11.0 microns to make adough-like mix which willpull and result in a' water-resistant porous composition of matter afterbeing prop erly heat treated. By changing the ratio ofthe filler to thesolution of silicate of soda the degree of porosity of the board changesand the water resistance varies to someextent. Decreasing the particlesize of'thefill- 1 er also decreases the proportion of filler. As anexample, a mix of one part silicate of soda and two parts dolomiticlimestone having an average particle size of 9.5 microns gives about thesame fineness of structure as a mix of one part silicate to 1.6 parts ofdolomitic limestone having an average particle size of 9.0 microns orabout 1.3 parts of dolomitic limestone having an average particle sizeof 8.4 microns. Increasing the viscosity of the sodium silicate solutionabove 2500 centi-.'

poises makes little change in the structure while commercial silicates,which are below 1000 centipoises, produce a-ooarse, weak, and easilydisintegrated structure.

Sodium silicate solutions above a viscosity of about 1000 centipoises at25 centigrade increase ra idly in viscosity for slight increases in eamount of dissolved silicate. We believe this is, of much importance inthis invention. As an example: in a solutioninwhich the ratio of Na,OtoSiO is2z82 size of between 8.4 and 11.0 microns.

I tions.

to 1, a difi'erence of water content of about 2 per cent raises theviscosity from 650 to 8000 centipoises. A solution of 2500 centipoisescontains only about 0.30 per cent more water than one of 8000centipoises.

In general, as the proportion of filler in the mix increases over thepreferred proportions, the water resistance of the structure falls off.This falling ofi .is small except where the structure becomes animportant factor. As the proportion of filler increases the structurebecomes finer, until finally a point is reached where the structurebecomes crumbly. The crumbly structure disintegrates easily in hotwater. As the proportion of filler in the mix is lowered, the structurebecomes more coarse until it will not stay together under ordinaryhandlin In general, we prefer to keep the ratio 0 filler to solution ofsilicate of soda below 2.2 to 1 and preferably between about 1.2 to 1and 2.2 to 1, the filler having an average particle If the solutionshave a viscosity greater than 2000 centipoises and the SiO -Na O ratiois between 2.6 to 1 and 3.4 to 1, then the solutions contain from 0.38to 0.17 arts of sodium silicate (anhydrous) for eac part of filler, thefiner particle sizes requiring the larger proportion of silicate. Thesefigures are based on the analysis of the sodium silicate solu- Solutionshaving a viscosity of be tween 2000 and 8000 centipoises will have thefollowing average sodium silicate content:

SlO Na O Sodium sillratlo cate content 2.6:1 46% 2.8: 1 44% 3.2: 1 40%3.4: 1 38% A dough-like mix at room temperature or about 25 0. should beused to secure best puffing results if the puffing heat is rapidlyapplied. This pufling is usuall secured by a temperature varying rom 120to usln 200 C. If the mix is made at higher than room temperature themix may be more fluid due to the lower viscosity of sodium silicate athigher temperatures. A thinner silicate than is necessary to produce adough-like mix may also be used to make the IIllX provided the amount ofsilicate in solution is suflicient to secure the proper pufiing action,and provided further, the excess water is evaporated prior to pufiingthereby giving a mix which is equivalent to the dough-like mix at 25 G.Our invention covers a doughlike mixture at 25 C. or the equivalentthereof at other temperatures or other concentrations of sodiumsilicate. A soap may also be incorporated in the mix to secure a betterpufiing action.

A porous mineral aggregate, such as 18 described in O. W. Storeyapplication, Serial No. 103,392, April 20, 1926, may be added to thedough-like mix and a moisture-resistant product obtained after heattreating the pulled product. Such an aggregate may be a porous slag butshould not ap reciably increase the ratio of the amount 0 sodiumsilicate solution to finel ground filler when incor orated therewit Suchan aggregate, WlllCll need not be porous, will not decrease the waterresistance of the resulting product but will decrease the cost bydecreasing the amount of sodium silicate. The sodium si1i cate-fillercomposition. acts as a binder or cement between the coarser particles ofaggregate.

Although our invention relates especially to a puffed, porous,composition of matter, it may also be applied to sodium silicatecompositions that are not pufi'ed or only slightly pufl'ed. If apuffable dough-like mix which is composed of a filler, such as a groundlimestone, or brick dust, having an average particle size of between 8.4and 11.0 microns, and a solution of high viscosity sodium silicate orits equivalent, is slowly air dried and then heated slowly to 210 0.,this composition of matter has excellent water resistance and is muchsuperior to those mixtures which are made with a coarser filler and aproportion of silicate not contemplated by our invention. Those mixtureswhich we have discovered to be highly resistant to moisture when thesodium silicate is nearly dehydrated will also show a much superiorwater resistance when allowed to harden at low temperatures.

Throughout the claims, the consistency of the dough-like composition ofmatter and the viscosity of the sodium silicate is specified at 25 C.()ur invention, however, is not limited to mixtures and solutions atthis temperature and covers mixtures of different consistencies andsodium silicate solutions of other viscosities at other temperaturesequivalent to the specified description at 25 C.

We claim:

1. A water resistant composition of matter comprising an intimatemixture of silicate of soda and a ground mineral filler, said fillerhaving an average particle size of between 8.4 and 11 microns.

2. A water resistant composition of matter comprising an intimatemixture of silicate of soda and ground limestone, the limestone havingan average particle size of between 8.4 and 11 microns.

' 3. A water resistant composition of matter comprising an intimatemixture of silicate of soda and a filler of ground dolomitic limestone,said filler having a maximum concentration of particle surface occurringbetween article sizes of 2.5 and 5 microns, said soluion of silicate ofsoda containing from 0.38 to 0.17 parts of silicate of soda for eachpart of filler.

4. A water resistant composition of matter comprising an intimatemixture of silicate of soda and a filler of ground limestone, saidfiller having an average particle size of be tween 8.4 and 11 micronsand being articularly free of particles less than 0.8 micron indiameter.

5. A dough-like mass for makings. water resistant composition of mattercomprising an intimate mixture of a solution of silicate of soda havinga viscosity of at least 2000 cenm tipoises at 25 C. and a ground mineralfiller said filler having an average particle size oi between 8. and 11microns.

6. The method of making a water resistant, hard porous structure ofsodium silicate and a ground mineral filler which comprises grindin thefiller so that its average particle size is etween 8.4 and 11 microns,mixing said ground filler with a solution of silicate of soda having aviscosity of not less than 2000 centipoises at C. to form a doughlikemass, and rapidly heating said doughlike mass to form a porousstructure.

7. The method of making a water resisting, hard porous structure ofsodium silicate 25 and a filler of limestone which comprises grindingthe limestone so that the average particle size is between 8.4 and 11microns, mixing the ground limestone with a solution of silicate of sodahaving a viscosity of not so less than 2000 centipoises at 25 C. to forma doughlike mass and rapidly heating said doughlike mass to form aporous structure. t In testimony whereof we afiix 0ur,signaures. OLIVERW. STOREY.

MAX KLIEFOTH.

